1. Field of the Invention
The present invention relates to a control unit for triggering a plurality of electric loads with a plurality of input signals, wherein the electric loads are triggered by means of pulse-width modulated signals and the input signals are pulse width modulate (PWM) signals. Furthermore, the invention relates to a method with which the control unit according to aspects of the invention triggers a plurality of electric loads with a plurality of input signals.
2. Description of the Related Art
The triggering of electric loads such as lamps, heating coils, step motors is frequently achieved with the aid of the pulse width modulation method (PWM method). Here, the power delivered to the load can be regulated or controlled by the current flowing into the load by means of pulse width modulation.
An essential advantage of PWM triggering is that the power losses in the triggering electronics can be kept at a low level by the switching operation of the PWM method. For this reason, the PWM method is frequently used in motor vehicles for triggering electronic load components such as lamps.
The PWM signals with which the power feed into the load is switched on or off are usually generated in motor vehicle control devices via timer modules which are integrated into the micro-controller, wherein the pulses of all PWM signals are switched on or are set to logical high at the same point in time, and depending on the PWM-signal duty cycle, can be switched off or set to logical low at different points in time.
This leads to a problem which is also a disadvantage of the PWM method, namely that when the pulses are switched on, very high switching peaks can occur with PWM signals. According to the prior art, different methods are represented in order to reduce these switching peaks with different possible embodiments.
Here, the switch-on time points are above all distributed within a cycle period in such a manner that the alternation portion and thus the attenuation are minimal, and at the same time, the fundamental wave of the resulting input current is as high as possible, and therefore the required limit frequency or attenuation is as high as possible. This can result in fixed phase relations due to the assignment of the switch-on time points.
However, if a plurality of regulation tasks is executed at the same time, i.e. if a plurality of electric loads are regulated or controlled by a corresponding number of PWM signals at the same time, the capacity required in the control electronics increases significantly, or the available computing capacity is reduced for each individual input channel.